emscripten: Another attempt at optionally having the canvas use whole window.

Fixes #11949.

include/SDL3/SDL_hints.h

@@ -753,6 +753,28 @@ extern "C" {
  */
 #define SDL_HINT_EMSCRIPTEN_KEYBOARD_ELEMENT "SDL_EMSCRIPTEN_KEYBOARD_ELEMENT"
 
+/**
+ * Dictate that newly-created windows will fill the whole browser window.
+ *
+ * The canvas element fills the entire document. Resize events will be
+ * generated as the browser window is resized, as that will adjust the canvas
+ * size as well. The canvas will cover anything else on the page, including
+ * any controls provided by Emscripten in its generated HTML file. Often times
+ * this is desirable for a browser-based game, but it means several things that
+ * we expect of an SDL window on other platforms might not work as expected,
+ * such as minimum window sizes and aspect ratios.
+ *
+ * This hint overrides SDL_PROP_WINDOW_CREATE_EMSCRIPTEN_FILL_DOCUMENT_BOOLEAN
+ * properties when creating an SDL window.
+ *
+ * This hint only applies to the emscripten platform.
+ *
+ * This hint should be set before creating a window.
+ *
+ * \since This hint is available since SDL 3.4.0.
+ */
+#define SDL_HINT_EMSCRIPTEN_FILL_DOCUMENT "SDL_EMSCRIPTEN_FILL_DOCUMENT"
+
 /**
  * A variable that controls whether the on-screen keyboard should be shown
  * when text input is active.